1. Field of the Invention
The present invention relates to a suspension device for an automobile employing a torsion bar which utilizes a bar torque, and more particularly, it relates to a suspension device comprising a torsion bar which has a function of varying its spring constant with a load.
2. Description of the Background Art
In general, a torsion bar which is employed in a suspension device for an automobile has a fixed spring constant. An automobile which is provided with a torsion bar having a small spring constant is comfortable to ride in when the same is empty or driven on a flat road with application of a small load. However, when such an automobile is significantly loaded or driven on an irregular road and the load applied thereto is increased, its operational stability is deteriorated. On the other hand, an automobile which is provided with a torsion bar having a large spring constant is uncomfortable to ride in although the same has high operational stability.
To this end, there have been proposed some torsion bars which can vary spring constants to be increased/decreased with loads.
Japanese Utility Model Laying-Open Gazette No. 57-35530 (hereinafter referred to as reference 1) discloses a torsion bar having a stopper, which projects from an intermediate portion along the axial direction of the torsion bar to be in contact with a stopper bearing provided in a position facing the stopper.
In the torsion bar of reference 1, the stopper bearing is fixed to a portion, such as a car body, other than the torsion bar. When the stopper comes into contact with the stopper bearing, therefore, a portion of the torsion bar between the fixed end and the stopper is so fixed that only the remaining portion, i.e., a portion between the stopper and the free end of the torsion bar, serves as a spring to reduce the effective length of the torsion bar. Thus, the spring constant of the torsion bar is increased.
Japanese Utility Model Laying-Open Gazette No. 59-102413 (hereinafter referred to as reference 2) discloses another type of torsion bar, in which an arm is fixed to an intermediate portion of the torsion bar and an end of the torsion bar is fixed to a part of a suspension arm, while a stopper is provided on another part of the suspension arm, to be in contact with the said arm when the torsion bar is twisted by a prescribed amount.
When the torsion bar of the reference 2 is twisted until the arm comes into contact with the stopper, a portion of the torsion bar between the arm and the end which is fixed to a part of the suspension arm is so fixed that only the remaining portion, i.e., a portion between the arm and the other end of the torsion bar, serves as a spring. Also in this case, the effective length of the torsion bar is so reduced as to increase the spring constant.
Japanese Utility Model Laying-Open Gazette No. 59-102414 (hereinafter referred to as reference 3) discloses a torsion bar assembly formed by combination of a hollow torsion bar and a solid torsion bar which is inserted in the hollow torsion bar. While the torsional amount of the torsion bar assembly is small, only the solid torsion bar serves as a spring. When the torsional amount reaches a prescribed value, on the other hand, the solid torsion bar engages with the hollow torsion bar through engaging portions to effectuate the spring constants of both torsion bars, thereby increasing the spring constant of the overall torsion bar assembly.
Japanese Utility Model Laying-Open Gazette No. 56-4908 (hereinafter referred to as reference 4) discloses not a suspension device itself but a stabilizer having a torsion bar, which is provided with a stopper member in its intermediate portion. One end of the stopper member is fixed to a part of a twisted portion of the torsion bar, and the other end is adapted to engage with the torsion bar in a position separated from the fixed portion at an angle exceeding a prescribed torsional angle of the torsion bar along the torsional direction.
When the torsion bar of the reference 4 engages with the stopper member due to application of a heavy load, the effective length of the torsion bar for serving as a spring is restricted to that of the portion other than the stopper member, thereby increasing the spring constant.
In reference 1, the stopper bearing for receiving the stopper, which is provided in the torsion bar, is fixed to the car body etc. In reference 2, on the other hand, the stopper for receiving the arm which is formed in the torsion bar is provided on the suspension arm. These torsion bars cannot change the spring constants by themselves. When these torsion bars are mounted on automobiles, therefore, it is necessary to simultaneously modify parts of the car bodies or the suspension arms in response to the torsion bars. Thus, these torsion bars have no generality as mechanism elements.
The device in reference 3 is complicated in structure since the solid torsion bar is assembled into the hollow torsion bar. Further, a section of a small spring constant, i.e., a section in which only the solid torsion bar serves as a spring, is restricted to such a range that the solid and hollow torsion bars engage with each other in the engaging portions from the separated state. This range is fixed and unchangeable.
The torsion bar of reference 4 must have a spring constant which is horizontally symmetrical with respect to the stopper member since the same forms a stabilizer. Consequently, the torsion bar forming the stabilizer must be uniform in thickness on both sides of the stopper member. Thus, variation of the spring constant is attained only by change in effective length of the torsion bar when the torsion bar engages with the stopper member, and it is difficult to greatly change the spring constant.
Further, it is impossible to displace the stopper member in the torsional direction of the torsion bar since one end of the stopper member is fixed to the torsion bar. Thus, the value of a load causing change in spring constant is rendered constant, and it is impossible to adjust a point of spring constant variation by service conditions such as the type of the automobile, the state of the road and the like.